Countershaft transmissions having a plurality of speed ratios in each direction of operation are particularly useful in the driveline of vehicles such as earthmoving wheel loaders, rubber tired log skidders, track-type tractors, and other off-highway heavy-duty vehicles. Such transmissions are advantageous in that a plurality of rotating clutches and associated gears can be so positioned on the usual parallel shafts as to allow considerable flexibility in adapting them to different vehicle space requirements. A considerable number of speed ratios can also be obtained with but minor changes to the transmission, while permitting a substantial number of similar parts to be used for manufacturing economy.
For example, the following United States countershaft transmission patents are of general interest to the art: U.S. Pat. No. 3,064,488 issued Nov. 20, 1962 to A. L. Lee et al; U.S. Pat. No. 3,080,767 issued Mar. 12, 1963 to S. J. Price, Jr.; U.S. Pat. No. 3,425,293 issued Feb. 4, 1969 to H. S. Krawczyk et al; U.S. Pat. No. 3,465,609 issued Sep. 9, 1969 to J. F. Fisher et al; U.S. Pat. No. 3,710,637 issued Jan. 16, 1973 to J. F. Fisher et al; U.S. Pat. No. 3,858,455 issued Jan. 7, 1975 to R. L. Sisson et al; U.S. Pat. No. 3,913,411 issued Oct. 21, 1975 to J. J. Jameson; and U.S. Pat. No. 4,341,127 issued Jul. 27, 1982 to E. Stodt.
While such countershaft transmissions have a considerable number of desirable features they are deficient in several other respects. One of the major problems with them is that if they are connected to the output member of the engine and/or optional torque converter assembly of the vehicle they require excessive space above the axis of the input shaft. Specifically, in some vehicular applications it would be necessary to raise the floor plates and elevate the entire operator station in order to obtain sufficient clearance above the input shaft's axis to accommodate large diameter components such as a rotating clutch. Another factor of significance is that some of these available transmissions have an excessive axial length and/or an excessive transverse width so that they cannot fit into the limited space available in a vehicle.
One type of countershaft transmission, such as that disclosed by U.S. Pat. No. 4,823,639 issued to Krause et al., and having an issue date of Apr. 25, 1989 provides a transmission structure facilitating a family of countershaft transmissions which lend to custom construction of each transmission to suit the particular usage and speed requirements specified for the vehicle.
However, it is common for a machine owner, having a machine employing one of the family of aforesaid transmissions, to require the machine to include more than one operational and speed range capability. For instance, a ground-engaging machine such as a wheel loader, for example, may require a low speed application such as mowing, and thereafter, require a high-speed application such as loading and transporting earth, rock, etc.
Known transmissions which include structure to accommodate disparate operational ranges typically include dog clutches or manual engaged gear meshes which require the vehicle, employing such a transmission, to be stopped or possess little if any speed when transitioning between operational ranges. For example, U.S. Pat. No. 3,916,714 issued to Sisson et al. and having and issue date of Nov. 4, 1975 discloses a sleeved shift-connecting member that is positionable between one of two positions. Accordingly, the selected gear assemblies, to provide the desired operational range, require to be intermeshed through the sleeve which, in turn, necessitates that the gears include negligible rotational speed to carry out the speed range shift.
Therefore, a countershaft transmission, of simple construct, which provides both a high range capability and a low range capability which significantly increases the versatility of the machine employing such a transmission, would be desirable. Furthermore, a transmission having dual range capabilities that may be shifted when the vehicle possesses a significant speed, would be desirable.